Scanning SQUID Microscope for Sensing Vector Magnetic Field

We designed a vector sensor for sensing magnetic fields by using a 3-dimensional (3D) scanning superconducting quantum interference device (SQUID) microscope. A vector sensor consists of three SQUID sensors, which are fabricated on the same chip and each SQUID sensor has a pick-up coils for X, Y, Z directions. Three coils with readout circuits are configured in orthogonal with each other to measure the magnetic field vector. We succeeded in fabricating some SQUIDs sensors with three pick-up coils. The critical current density Jc of a Josephson junction (JJ) is 320 A/cm² and the minimum critical current Ic of JJ becomes 12.5 μA. We have also designed a prototype model of the instrument. We use an XYZ piezo-driven scanner for controlling the position of the pick-up coils in the range of 5 mm x 5 mm at low temperatures. Two heaters are installed for controlling the temperatures of a sensor and a sample. The room-temperature electronics can control three-channel SQUIDs simultaneously, and has the bandwidth of 6 MHz.